ABSTRACT Childhood overweight and obesity (OW/OB) is a significant public health burden, affecting one third of U.S. children ages 6 through 19. Childhood OW/OB is associated with numerous adverse health outcomes, including increased risk of cardiovascular disease and diabetes, which often persist into adulthood. Among this population, poor sleep health is also highly prevalent, and poor sleep health is suggested to be a putative risk factor for the development of OW/OB, especially among children. Previous studies examining the association between sleep and OW/OB risk have been limited by a singular focus on `usual' sleep duration as the sole indicator of an individual's sleep health. However, a growing number of studies have brought into question the importance of other sleep health dimensions, such as sleep schedule and quality, as well as the role of night- to-night variability in sleep health, which may impact OW/OB risk independent of sleep duration. This suggests that focusing on usual sleep duration alone may mask other critical dimensions of sleep health influencing OW/OB risk over time. Furthermore, although diet is a suggested behavioral pathway through which poor sleep may impact obesity risk, previous studies have largely failed to explore the impact of night-to-night variability in sleep on weight-related behaviors, such as dietary intake, occurring the following day. If findings support the proposed study hypotheses, the identification of variability in sleep health as a key factor influencing daily weight-related behaviors will increase our understanding of the role of sleep in OW/OB risk, and inform future prevention and intervention programs targeting obesity and its associated health problems in children. This project will leverage data from 200 children (ages 8-12 at baseline) enrolled in the NIH-funded Mothers' and their Children's Health (MATCH) Study, with EMA-assessed sleep and 24-hour recall-assessed dietary intake during week-long data collection waves, occurring bi-annually across three years (6 waves total). This study design allows for the elucidation of the temporal, short- and longer-term associations among sleep, diet, and OW/OB risk. Specifically, project analyses will use multilevel modeling and mixed effect location scale modeling to examine the short-term effects of sleep health on a given night with dietary intake the following day, as well as the cross-sectional and longitudinal effects of sleep and its variability on overall diet and obesity status and trajectories. This project also proposes a sleep sub-study in a sample (n=30) of MATCH children to determine the correspondence of wrist-worn accelerometer with EMA measures of daily sleep and to assist in data interpretation and cross-study comparisons.